Several groups have developed high intensity focused ultrasound systems for treatment of BPH in prostate. Most of these approaches, including that currently used by the applicant company, utilized fixed focus ultrasound transducers that are moved mechanically to treat the desired volume of tissue. Some groups are investigating the use of phased arrays to provide electronic steering of the focal region in at least one dimension to reduce the mechanical movement of the transducer and to allow rapid movement of the focus. Most of these systems use small elements to eliminate grating lobes and thus require a large number of elements. It is proposed in this study to use a smaller number of large elements to reduce the cost and complexity of manufacture, but to make use of random location and/or size of elements to reduce grating lobes to an acceptable level. The design of such an array will first be examined theoretically and then an experimental prototype will be constructed and tested. In Phase II, the results of Phase l studies will be used to guide the design of a transducer and incorporated imaging system for testing in animals. PROPOSED COMMERCIAL APPLICATIONS: The treatment of BPH is very common in the later years. The longer a man lives the more likely it is that he will need to be treated for BPH or prostatic cancer. Thus, there is a large market for a system which will provide this treatment in an economical and painfree manner. This company currently manufactures such a system utilizing a fixed focus system. However, the use of phased array technology with a limited number of elements could provide a significant improvement over existing commercial systems which do not used phased array techniques.